1. Field of the Invention
The embodiments of the invention generally relate to medical devices and assemblies, and more particularly to an orthopedic surgical implant assembly used in the field of surgical lumbar, thoracic and cervical spine treatment.
2. Description of the Related Art
Surgical procedures treating spinal injuries are one of the most complex and challenging surgeries for both the patient and the surgeon. When there are various deformities, trauma, or fractures of the vertebra, surgeons may attempt to “fuse” them together by attaching screw-like devices into the pedicles of the spine and thereby connecting several vertebrae (typically two or more) using a semi-rigid rod. However, due to the complexity of the human anatomy, most surgeons must bend the rod (causing notches thereby reducing fatigue resistance) before placing them into two or more non-aligned pedicle screws in order to properly stabilize the pedicle screw assembly within the patient's body. However, this bending causes notches and reduces fatigue resistance and wastes valuable surgery time before the surgeon is able to insert the rod. That is, the surgeon must sacrifice the freedom of optimal screw placement in the spine for ease of construct assembly.
Depending on the purpose of the spine surgery, indications, and patient size, surgeons must pre-operatively choose between different spinal systems with differing rod sizes pre-operatively sometimes causing delays in surgery while waiting for more adequate systems to be sterilized. Some surgeons prefer monoaxial screws for rigidity, while some sacrifice rigidity for surgical flexibility in screw placement. Therefore, a system is needed to accommodate both theories. For example, during scoliosis surgery conventional polyaxial systems typically cannot lock into a desired position to persuade the spinal column into the desired correction before final construct assembly.
Most conventional top loading polyaxial spine screws do not do enough to address cantilever failure of the assembly components. Additionally, most conventional polyaxial screws generally do not offer enough flexibility because the rod sits too closely on top of the center of rotation of the bone screw producing a smaller are of rotation. Moreover, most conventional polyaxial screw assemblies do not offer enough freedom and have too much of a “fiddle factor” in fabrication. Additionally, most conventional pedicle screw assemblies depend on deforming and notching the rod to lock it axially and rotationally to the screw head thereby reducing the life of the rod by increasing the mechanical fatigue of the rod. Thus, there remains a need for a new and improved pedicle screw assembly capable of overcoming the limitations of the conventional designs thereby providing the surgeon with improved intra-operative flexibility and the patient with an improved prognosis for better and complete rehabilitation.